Stabilizing chloroethylene polymers with cadmium hydroxy laurate and lead stearate



United States Patent M STABILIZING CHLOROETHYLENE POLYMERS WITH CADMIUMHYDROXY LAURATE AND LEAD STEARATE Erwin M. Jankowiak, Midland, andAlfred R. Nelson,

Bay City, Mich, assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Application February 10, 1956 SerialNo. 564,636

6 Claims. (Cl. 260-23) This invention relates to a new and improvedprocess for stablizing haloethylene polymers against thermaldegradations. The invention likewise includes the stabilizedcompositions produced in accordance with that process.

Haloethylene polymers, such as polyvinyl chloride, are commonlyfabricated into useful articles by thermal fabrication methods.Additionally the articles fabricated from haloethylene polymers arefrequently exposed to relatively high temperatures for prolonged periodsof time. It is common knowledge that such haloethylene polymers and thearticles produced therefrom are seriously degraded by a loss of HCl fromthe polymer chain when exposed in the unstabilized condition to theelfects of heat. That degradation which exhibits itself as adiscoloration and a reduction in properties is rapid and in a very shorttime can render the polymer or the article commercially useless. Theprior practice has been to blend certain additives with the polymer tostablize the polymer to elevated temperatures. Blending operations aretime-consuming since the additive must be uniformly distributedthroughout the polymer mass and are costly because of the capitalinvestment required for equipment, the manpower required and thehorsepower used. It would be desirable if the additives could beincorporated into the monomer charge prior to polymerization. Moststabilizers however inhibit or seriously retard polymerization,destroying any economic advantage.

It is the principal object of this invention to provide an improvedprocess for stabilizing haloethylene polymers to the degradative effectsof elevated temperatures.

It is a further object to provide such a process for stabilizinghaloethylene polymers which will eliminate the costly and time-consumingblending operations.

It is a still further objectto provide a stabilized composition based onhaloethylene polymers which has improved resistance to the degradativeelfects of elevated temperatures. The above and related objects areaccomplished by means of a process consisting of the preparation of apolymerizable charge comprising haloethylene monomers, polymerizationcatalyst, and certain heat stabilizers dispersed in non-emulsifiedaqueous suspension, subjecting that charge to polymerization conditionswith agitation and thereafter recovering the polymer. The inventionlikewise includes compositions based on haloethylene polymers containingthe heat stabilizers.

The haloethylene polymers which may be employed in the process andcompositions of this invention are any polymers and copolymerscontaining halogen substituents and prepared from vinyl monomers.Typical examples of such polymers are the polymers of vinyl chloride andvinylidene chloride, the copolymers of vinyl chloride and vinylidenechloride, and the copolymers of either vinyl chloride or vinylidenechloride Wih another copolymerizable monomer, such as vinyl acetate oracrylonitrile. The polymers and copolymers of vinyl chloride and2,905,719 Patented Sept. 29, 1959 ICC vinylidene chloride present thegreatest problem in heat stability and are preferred.

The preparation of polymers in non-emulsified aqueous suspension is oldin the polymerizationart. Typically a monomer or a mixture of two ormore comonomers is dispersed in an aqueous medium containing a watersoluble dispersing agent, such as certain cellulose ethers.Polymerization is initiated and maintained by means of a polymerizationcatalyst, such as benzoyl peroxide or lauroyl peroxide, at a temperatureof from 30 C. to 70 C. The polymerization system is commonly agitatedthroughout polymerization to help maintain the dispersion and to helpthe heat transfer characteristics of the system. Following completion ofthe polymerization the polymer is recovered by filtration orcentrifuging and then dried. The heat stabilizer to be used in theinvention consists of a combination of lead stearate, together withcadmium alpha-hydroxylaurate. That compound is sold commercially asP-1576 by Advance Solvents and Chemicals Co. and may contain traceamounts of cadmium alphahydroxy myristic acid. The lead stearate may beeither n-lead stearate or dibasic lead stearate, although n-leadstearate is the most efiicient and accordingly is preferred. Thecombination of the two ingredients exhibits a synergistic eifect inthermally stabilizing haloethylene polymers that far surpasses anyprediction of their stabilizing effectiveness.

Each of the ingredients of the heat stabilizer may be used in amounts offrom 0.5 to 4 percent by weight based on the weight of the polymer, withthe percentage of the combined ingredients not to exceed 5 percent ofthe weightof the polymer. The ingredients may be used in any combinationof percentages providing the above limitations are observed. It shouldbe apparent that some polymers, such as those composed predominantly ofvinylidene chloride, are less resistant inherently to the degradativeeffects of heat and consequently will require correspondingly morestabilizer to arrive at a given degree of resistance. An investigatorwill be able to determine the optimum amount of stabilizer required forany polymer by simple preliminary experimentation. When less than 0.5percent of each ingredient is employed the eifectiveness of thestabilizer is so low that the thermal resistance imparted to thecomposition is negligible. When greater amounts than 5 percent of thestabilizer are used there are no additional benefits which accrue to thecomposition and some of the properties, such as strength and clarity maysuffer.

The manner in which the stabilizer is added to the polymerization chargeis unimportant. It has been found to be most convenient to add bothingredients to the aqueous phase prior to the introduction of themonomer especially when volatile monomers such as vinylidene chlorideand vinyl chloride are being used.

The heat stabilizer of this invention may be employed in compositionsbased on haloethylene polymers which likewise contain the other commonadditives which are blended with such polymers to produce commercialformulations. Thus, the stabilizer may be used in plasticized, filled,and pigmented compositions which likewise contain stabilizers for thepolymer against the eifects of light. The process and composition ofthis invention have an additional advantage when such compositions areprepared, since the heat stabilizer is intimately distributed throughoutthe polymer prior to blending into the composition of the plasticizers,pigments, fillers, and the like. Such blending is frequently carried outon hot mills which would have a serious efiect on the thermal life ofthe polymer if an unstabilized polymer was employed. Additionally n-leadstearate acts as a lubricant to prevent sticking of the composition tothe hot rolls of the mill. Still further, the polymers resulting fromthis process 3 have a greater porositythan unstabilized polymers, re-'sulting in a more rapid and uniform distribution of the other additivesinto the polymer.

By way of example several polymerization charges against the degradativeeffects of heat comprising the addition to the chloroethylenic monomerprior to polymerization of at least 0.5 percent by weight of leadstearate and at least 0.5 percent by weight of cadmium were preparedconsisting basically of 100 parts of water, 5 alpha hydroxylaurate theag gregate we1ght of both ing s3: z gg i f igigj g li gg iqfi gg gi gigredients not to exceed 5 percent by weight of said the charges was leftas a blank. To some of the charges monomer .dlspersmg Salli mpnomerand.sald Ingredients were added varying amounts of the ingredientscompris together w th a polymerization catalyst 1nto an aqueous ing thestabilizer of this invention. To others were added a subleFfmg the 3dlsperslon to P amounts of only one of the ingredients The chargeszation conditions recovering the polymer formed, and were prepared bymixing the stabilizer into the monomer finally dl'ylng Said P l/ andcatalyst and adding that to an aqueous phase con- 2. The process claimedin claim 1 wherein the chlorotaining the cellulose ether. Polymerizationwas initiated ethylene monomer is vinyl chloride. and maintained byheating the charge to 50 C. with agi- 3. The process claimed in claim 1wherein the chlorolatlOIl 15 hOuTS- The P ym was fi t washefi ethylenemonomer consists of a mixture of vinyl chloride several times withwater, and dried. PcIaS'EICIZCd composiand vinylidene ch10ride g gg pgjg g g gi i gg g g pgyg g g g 4. A thermally stable composition of mattercomprisparts of dioctyl phthalate. The compositions were com- 22 3 33}:g f g l g g g 21 32: 22: pression molded into test specimens and thespecimens p y g exposed in a convection oven at for 3 hours .sisting oflead stearate and cadmmm alpha-hydroxy or more. Periodically thespecimens were visually exlaurate' amined for discoloration. The resultsare shown in the The composltlon Claimed 111 clalm 4 Whereln thefollowing table. 25 chloroethylene polymer is polyvinyl chloride.

Table Percent by weight of Color after exposure polymer Original colorCadmium n-Lead alpha- 1 hour 2 hours 4 hours steal-ate hydroxyluurate 00 Light tan Brown Darkhrowm- 1 0 Colorless o 2 0 do do do 0 4 do T BrownDarkbrown.

1 1 do Colorless Cnlnr e Light tan.

1 2 do do do DO.

2 2 do do do D0.

The results indicate very clearly the outstanding stabil- 6. Thecomposition claimed in claim 4 wherein the ity imparted to thecompositions when both of the inchloroethylene polymer 1s a copolymer ofvinyl chloride gredients of the stabilizer are present as compared toand vmylldene chloride. that imparted when only one of the ingredientsis present UNITED STATES PATENTS Similar results were obtained whencompositions were References Cited in the file of this patent prepcopolymers of vinylidene chloride and 2,075,543 Reed et a1. Mar. 30,1937 vin c on e.

i claim. FOREIGN PATENTS 1. A process for stabilizing chloroethylenepolymers 599,429 Great Britain y 11, 1944

1. A PROCESS FOR STABILIZING CHLOROETHYLENE POLYMERS AGAINST THEDEGRADATIVES EFFECTS OF HEAT COMPRISING THE ADDITION TO THECHLOROETYLENIC MONOMER PRIOR TO POLYMERIZATION OF AT LEAST 0.5 PERCENTBY WEIGHT OF LEAD STEARATE AND AT LEAST 0.5 PERCENT BY WEIGHT OF CADMIUMALPHA-HYDROXYLAURATE, THE AGGREGATE WEIGHT OF BOTH INGREIDIENTS NOT TOEXCEED 5 PERCENT BY WEIGHT OF SAID MONOMER, DISPERSING SAID MONOMER ANDSAID INGREIDIENTS TOGETHER WITH A POLYMERIZATION CATALYST INTO ANAQUEOUS PHASE, SUBJECTING THE SO-FORMED DISPERSION RO POLYMERIZATIONCONDITIONS, RECOVERING THE POLYMER FORMED, AND DINALLY DRYING SAIDPOLYMER.